This drawing taken from a recent patent by Aharon Zidon of Givatayim, Israel, demonstrates how a diamond can be marked with a unique pattern by exposure to a radioactive isotope. A mask (lower drawing) is placed between the diamond and a small amount of radium so that as the radium decays, it implants daughter isotopes in the desired pattern.

Ever since concerns about the use of diamonds to support armed conflicts, terrorism, and other illicit activities arose in the early 2000s, the industry has been in search of methods that would allow the tracking of individual diamonds from source to market (see, e.g., A. A. Levinson and J. E. Shigley, “White House Conference on ‘conflict diamonds,’” S pring 2001 Gem News International, pp. 64–66). Given the potential commercial value of a practical and reliable method of diamond “fingerprinting,” it is not surprising that various individuals and groups have recently sought patents in this area.

However, of the possible methods discussed at the 2001 White House Conference, U.S. patents have been issued only for those that record internal characteristics via optical examination or that mark a diamond using a laser or radioactive isotopes. No techniques appear to have been patented recently in the U.S. for fingerprinting by X-ray topography, ion implantation, or spectroscopic or chemical analysis of inclusions or coatings.

Following is a summary of U.S. patents and patent applications for methods of diamond fingerprinting that have been awarded or published since the White House Conference in January 2001, in order of publication.

Lalit K. Aggarwal of Philadelphia received a patent for an “automated” diamond grading device (L. Aggarwal, Apparatus and Method for Grading, Testing, and Identifying Gemstones, U.S. patent 6,239,867, issued May 29, 2001). The grading device, known as ImaGem, records several attributes of a diamond within a computer-controlled imaging apparatus. Once a diamond has been scanned, another instrument, known as VeriGem, can be used to identify it later by matching it to stored information. Grading a diamond with ImaGem takes about five minutes; identification with VeriGem takes approximately 20 seconds. Both devices will be marketed by Imagem Inc., also of Philadelphia. The company says that ImaGem will be available in 2004, while VeriGem is currently being beta-tested and is scheduled for release in 2005.

Aharon Zidon of Givatayim, Israel, has received a patent for a method of marking diamonds (and other objects) with radioactive isotopes in a specific pattern (A. Zidon, Apparatus for and Method for Marking Objects, Objects Marked Thereby and Apparatus and Method of Reading Marked Objects, U.S. patent 6,616,051, issued September 9, 2003). With this method, as illustrated in the figure, the pattern is applied by masking the diamond in front of a small quantity of radium such that, as it releases radioactive “daughter” isotopes through radioactive decay, these are implanted in a precise pattern in the diamond.

A team from Lazare Kaplan International, New York, has received a patent on a new method of laser inscribing gemstones (G. R. Kaplan et al., Microinscribed Gemstone, U.S. patent 6,684,663, issued February 3, 2004). This patent describes several methods of encrypting and authenticating laser inscriptions that could be useful for diamond fingerprinting.

Most recently, Malcolm Warwick of Vancouver, Canada, has submitted a patent application for a method that uses confocal laser interferometry to determine the relative positions of inclusions in a diamond (M. R. Warwick, Method and Apparatus for Identifying Gemstones, U.S. patent application 20030223054, published December 4, 2003). With this method, the diamond is scanned by a laser beam, and the position and orientation of inclusions are recorded in a unique profile, which can be encoded in a laser inscription on the stone’s girdle. The process is currently being developed by Canadian Gem ID Systems, also of Vancouver.